Nothing grounds you like good breathing. If you find yourself getting stressed, heady, disconnected, anxiousor over-thinking then take a moment (go to the loo to do it if necessary) and focus on your breathing for a few moments.
Breathe into your belly (aim for the belly button) and take a few slow breaths. As you breathe out you can blow out any stress or discomfort you are feeling in the body.
It's amazing how calming and grounding this exercise is.